Corrected the JavaDoc of Widget#doAttach/DetachChildren() to reflect its actual usage.  The old comment stated that all implementors of HasWidgets must override it.  In fact, it only needs to be overridden if a child widget is physically but not logically attached to a parent.

Patch by: jlabanca
Review by: sumitchandel



git-svn-id: https://google-web-toolkit.googlecode.com/svn/releases/1.6@4377 8db76d5a-ed1c-0410-87a9-c151d255dfc7